When a strip is being rolled, tension differences can occur between the strip edges of the strip. One of the substantial causes of the tension differences is a wedge in the strip profile. A wedge in the strip profile can have various causes. Thus, for example, the strip can already have a wedge-shaped profile before being rolled. Alternatively, the wedge can be caused by the rolling in the roll gap. A plurality of causes come into discussion for lending the strip a wedge-shaped profile. For example, the strip can have a wedge-shaped temperature distribution and the strip can enter the roll gap eccentrically, or the roll gap itself can be wedge-shaped. Combinations of these (and other) causes are also possible.
It is known in the prior art to acquire the stress differences occurring in the strip by arranging between two respective stands a loop lifter that is equipped with force transducers on both side arms. However, conventional loop lifters have only lateral force measurement, and therefore deliver only a total force, but not a differential force between the two strip edges. The tension distribution in the strip is therefore unknown without a loop lifter with force sensors on both sides. It is therefore impossible to predict the direction in which the strip is deflected when the strip foot of the strip runs out of one of the rolling stands. However, particularly at the rear stands of a multistand rolling train an adjustment of the swivel value or other control elements of the rolling stand arranged directly downstream of the respective rolling stand is not possible quickly enough in order to prevent the strip foot from striking against a side guide of the rolling train.
Furthermore, it is known in the prior art for a controller of the rolling train to track the strip head visually as the strip is being threaded in and—in accordance with his personal impression of strip position and strip corrugation—to set the adjustment of the rolling stand currently being run through by the strip head (in particular a swivel position of the rollers).